The invention relates to a high-pressure gas discharge lamp comprising a translucent lamp vessel, which is sealed in a vacuum-tight manner and is filled with an ionizable gas. The lamp has electrodes projecting into the lamp vessel connected to current supply conductors which extend to the exterior through the wall of the lamp vessel. At least one electrode comprises a rod of mainly tungsten, which has near its tip projecting inside the lamp vessel a helical winding of wire of mainly tungsten. A first layer of turns is arranged to surround the rod and an outer layer of turns is arranged to surround the first layer. The first layer of turns locally having a turn of high pitch P being at least equal to the wire diameter of the first layer of turns plus the wire diameter of the outer layer of turns. The winding is fixed on the rod. Such a lamp is known from U.S. Pat. No. 3,170,081.
The purpose of the winding around the electrode rod is to obtain a satisfactory temperature variation over the electrode or to hold electron-emitting material.
It is necessary to fix the winding on the rod, for example by deforming a turn in the hot state so that it clamps around the rod, or by welding the winding locally to the rod.
In the lamp according to the aforementioned U.S. Pat. No. 3,170,081, the first layer of turns is a body, which is slipped with a certain amount of clearance around the electrode rod and is fixed on it by deforming the layer in the hot state, while the outer layer of turns is a separate body slipped around the first layer. In order to fix the second layer of turns, the first layer of turns has a projecting wire portion at its end remote from the tip of the electrode rod, while the outer layer of turns has at the corresponding end a wire portion bent towards the rod. This electrode construction renders it difficult to manufacture the electrodes and therefore the lamp.
The non-prepublished European patent application No. 86201239.0 corresponding to U.S. application Ser. No. 884,699, of the Applicant discloses a lamp of the kind described in the opening paragraph, in which the outer layer of turns of the winding of the electrode grips at least twice around a turn of high pitch of the first layer, while forming an equal number of contact areas and engaging with clamping fit the electrode rod at least substantially diametrically opposite to those contact areas. The turn(s) of the outer layer of turns gripping around a turn of high pitch of the first layer has (have) a pitch corresponding to the pitch of the remaining turns of the outer layer of turns, i.e. equal to the wire diameter.